Biomedical subjects

T P Pons

Publications and source records attributed to T P Pons.

23 records · Page 2Linked to original sources

PubMed1986

The relationship of corpus callosum connections to electrical stimulation maps of motor, supplementary motor, and the frontal eye fields in owl monkeys.

Microstimulation and anatomical techniques were combined to reveal the organization and interhemispheric connections of motor cortex in owl monkeys. Movements of body parts were elicited with low levels of electrical stimulation delivered with microelectrodes over a large region of precentral cortex. Movements were produced from three physiologically defined cortical regions. The largest region, the primary motor field, M-I, occupied a 4-6-mm strip of cortex immediately rostral to area 3a. M-I represented body movements from tail to mouth in a grossly somatotopic mediolateral cortical sequence. Specific movements were usually represented at more than one location, and often at as many as six or seven separate locations within M-I. Although movements related to adjoining joints typically were elicited from adjacent cortical sites, movements of nonadjacent joints also were produced by stimulation of adjacent sites. Thus, both sites producing wrist movements and sites producing shoulder movements were found next to sites producing digit movements. Movements of digits of the forepaw were evoked at several locations including a location rostral to or within cortex representing the face. Overall, the somatotopic organization did not completely correspond to previous concepts of M-I in that it was neither a single topographic representation, nor two serial or mirror symmetric representations, nor a "nesting about joints" representation. Instead, M-I is more adequately described as a mosaic of regions, each representing movements of a restricted part of the body, with multiple representations of movements that tend to be somatotopically related. A second pattern of representation of body movements, the supplementary motor area (SMA), adjoined the rostromedial border of M-I. SMA represented the body from tail to face in a caudorostral cortical sequence, with the most rostral portion related to eye movements. Movements elicited by near-threshold levels of current were often restricted to a single muscle or joint, as in M-I, and the same movement was sometimes multiply represented. Typically, more intense stimulating currents were required for evoking movements in SMA than in M-I. A third motor region, the frontal eye field (FEF), bordered the representation of eyelids and face in M-I. Eye movements elicited from this cortex consisted of rapid horizontal and downward deviation of gaze into the contralateral visual hemifield.

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PubMed1985

The somatotopic organization of area 2 in macaque monkeys.

Area 2 is a traditional architectonic subdivision of anterior parietal cortex in macaque monkeys, but its overall somatotopic organization and responsiveness to different types of somatic stimuli are poorly understood, and there are uncertainties concerning its rostral and caudal extent. The goals of the present study were to define the rostral and caudal borders of area 2 better, and to describe its overall organization and responsiveness. Somatic receptive fields were defined for hundreds of closely spaced microelectrode recording sites in postcentral parietal cortex of individual macaque monkeys anesthetized with ketamine. Electrophysiological and architectonic evidence suggested that a 3-4 mm-wide strip of cortex along the caudal border of area 1 includes all or most of area 2. The most lateral explored portion of area 2 adjoined the representation of the face in area 1. Much of this sector of area 2 was activated by cutaneous stimulation of the face, especially the chin, but more caudal parts of the head also were represented there. Medially, an adjacent sector of area 2 represented the hand. Rostrally, in the cortex within 1.5 mm from the area 1 border, the glabrous surfaces of digits 5 through 1 were represented in a mediolateral cortical sequence, and from tip to base in a rostrocaudal sequence, mirroring the organization in the adjacent portion of area 1. More caudally at this mediolateral level of area 2, digit tips and other phalanges were represented for a second time. The pads of the palm and the dorsal surfaces of the hand were represented laterally and medially within the portion of area 2 devoted to the hand. More medially, the wrist, forearm, and arm were represented in a lateromedial cortical sequence in area 2, roughly matching the mediolateral organization within the bordering area 1. However, immediately caudal to the representation of the occiput, neck, and shoulder in area 1, a rostrocaudal strip of cortex extending across area 2 represented the arm and forearm for a second time in area 2. This cutaneously activated strip of cortex extended into area 5, where the proximal portion of the hand was represented. More medially, next to the trunk representation in area 1, area 2 was devoted to the trunk and limbs. Next to the representations of the ankle, leg, and thigh in area 1, area 2 was activated from similar locations on the hindlimb.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1985

Connections of area 2 of somatosensory cortex with the anterior pulvinar and subdivisions of the ventroposterior complex in macaque monkeys.

The principal goal of the present study was to determine the thalamic connections of area 2 of postcentral somatosensory cortex of monkeys. The placement of injections of anatomical tracers (horseradish peroxidase, wheat germ agglutinin, or 3H-proline) was guided by extensive microelectrode maps of cortex in the region of the injection site. These maps identified the body parts represented in the cortex included in the injection site, and provided information about the physiological boundaries of area 2, which was related later to the cortical architecture. Most injections were placed in the representation of the hand in area 2, which was highly responsive to cutaneous stimuli and could be mapped in detail. Injections were also placed in other parts of area 2, area 1, or area 5, and some injections involved more than one area. As other investigators have determined, regions of retrograde and anterograde thalamic label overlapped, demonstrating that connections with cortex are reciprocal. Injections completely confined to area 2 consistently produced label in two locations: the anterior pulvinar (Pa) and a dorsal capping zone of the ventroposterior complex that we term the ventroposterior superior nucleus (VPS). Single restricted injection sites resulted in one region of label in VPS, and multiple foci of label in Pa. In some cases where the injection was confined to the representation of the hand in area 2, label was also found more ventrally in the ventroposterior complex in ventroposterior nucleus proper (VP). Thus, area 2 receives input from Pa, VPS, and, at least in some locations and individuals, VP. Injections of tracers into area 1 confirmed previous findings that area 1 is densely interconnected with VP. In addition, there appear to be sparse connections with VPS. There was no evidence of connections with Pa. Evidence from injection sites that extended from area 2 into areas 5 and 7, and from injection sites in area 5, indicates that the lateral posterior nucleus (LP) projects to rostral areas 5 and 7. The results support the conclusion that area 2 is a functionally distinct subdivision of somatosensory cortex, and indicate that area 2 has thalamic connections that are characteristic of both "sensory" (VP and VPS) and "association" (Pa) cortical fields.

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PubMed1985

A sequential representation of the occiput, arm, forearm and hand across the rostrocaudal dimension of areas 1, 2 and 5 in macaque monkeys.

Receptive fields were determined for recording sites in cortical areas 1, 2 and 5 in macaque monkeys. While a mixture of cutaneous and deep receptors were represented in most regions of area 2, a specific mediolateral level of area 2 was highly responsive to cutaneous input. Anteroposterior rows of recording sites across areas 1, 2 and 5 at this mediolateral location revealed a continuous sequence of cutaneous receptive fields proceeding from the occiput and face in area 1 to the forearm and hand in area 5.

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PubMed1983

The relation of corpus callosum connections to architectonic fields and body surface maps in sensorimotor cortex of new and old world monkeys.

Corpus callosum connections of parietal and motor cortex were studied in New World owl monkeys (Aotus trivirgatus) and Old World macaque monkeys (Macaca fascicularis) after multiple injections of 3H-proline and horseradish peroxidase, HRP, into one cerebral hemisphere, and extensive microelectrode mapping of architectonic Areas 3b, 1, and 2 of the other hemisphere. Results were obtained both from parasagittal brain sections cut orthogonal to the brain surface and from sections from flattened brains cut parallel to the brain surface. Cortical fields varied in density of callosal connections, and the density of connections varied according to body part within sensory representations. Thus, Area 3b had few, Area 1 had more, and Area 2 had relatively dense callosal connections. Within each of these fields, connections were much less dense for the representations of the glabrous hand and foot and much more dense for the representations of the face and trunk. For the representation of the hand, retrogradely labeled cells were extremely sparse in Area 3b, moderately sparse in Area 1, and moderate in Area 2. There were less dense callosal connections in the hand representations of Areas 3b, 1, and 2 in macaque as compared to owl monkeys. Label in posterior parietal cortex was uneven with zones of extremely dense connections. A large region of very dense callosal connections was noted in motor cortex just medial to the probable location of the hand representation. In all regions, callosally projecting cells appeared to be more broadly distributed than callosal terminations. In no region was the discontinuous arrangement of callosal connections obviously organized into an extensive pattern of mediolateral or rostrocaudal bands or strips.

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